List the sequence of call events and return events from time moment 2 to time mo

Question

List the sequence of call events and return events from time moment 2 to time moment 3

• Constructor C(A x) in class C is invoked (call event)

• ?? [multiple steps here]

• The call to constructor C(A x) returns (return event)

• Constructor B(A x) in class B is invoked (call event)

• ?? [multiple steps here]

• The call to B(A x) returns (return event)

Basically, you need to fill in the blanks with the rest of the events. Describe precisely which method/constructor in which class is called/returns at each step. Do not omit any events—all calls and returns that happen during this execution should be described in the sequence.

*Note: This is not a coding question, rather a question that traces code. Please do not answer with a program/code. Use the information provided below to retrieve the answer:

Consider the following Java code: abstract class A private A h; public A(Ax)( this.h-x; if (x != null) x.set(this); } // constructor public A gereturn this.h; public void set (A y) { this. h = y; time moment 1.5 public abstract A p) public static void q(A x) A y yx.get() A z; z-y.p); public void r) Ax; xthis.get() q(x) class B extends A public B(A x)super(x): /constructor: calls A(A x) public A p)return this; class C extends B public C(A xsuper(x); //constructor; calls B(A x) public A get) return this; public A p) f Ax; x this.get ): return x; 1 class Main public static void main(String args) Ax, y: time moment 1 x - new C(null) time moment 2 time moment 3 y new B(x)

Explanation / Answer

When x = new C(null) is called then the null is passed to the constructor of class C.

The contructor of class C accepts an object of class and as we have passed the null object to the class C constructor hence it will accept it. The contructor of class C will pass the null object to it's parent class B using the statement super(x).

The constructor of the class B also accepts the null object and passes it on to it's parent class A.

The class A accepts the null object and saves it in the local variable h which is also an object of the class A. Inside the constructor of class A as the value of x is null, hence the if condition is not satisfied hence the statements inside the if are not executed.

Now the control returns to the main method.

Now the statement y=new B(x) is executed.

The contructor of class B is invoked and the object x is passed to the contructor of class B. Which further passes the object to it's parent class A.

The value of h is now equals to x. As x is not null hence this time the condition is satified and the set method of class A is called.

This time the value of h is set to y which was previously stored to x.

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